The present application is a National Phase application of PCT/GB99/03253 filed on Sep. 30, 1999 and published in English, which claims priority from Applications GB 9823138.4 filed on Oct. 23, 1998 and GB 9920342.4 filed on Aug. 28, 1999.
The present invention relates generally to a seal for a closure, and more specifically to a seal for sealing an aperture in a closure through which more than one elongate article may extend. The present invention also relates to closures including such a seal, and to seal parts constituting such a seal.
The present invention finds particularly utility as a seal for use in a casing for protecting junctions between elongate articles such as pipes, tubes or cables. As used in this specification the term xe2x80x9ccablexe2x80x9d will be understood to refer not only to electrically conductive cables, but also to bundles of optical fibres. When it is necessary to make end-to-end or branch connections between elongate articles such as pipes, tubes or cables the junction or splice where such articles are joined is almost always less strong and less resistant to environmental agents than is the article itself. Unless protected from such environmental agents, therefore, the junction between the elongate articles is subject to deterioration over time.
In telecommunication or power transmission systems it is frequently necessary to make splices either to join cables end-to-end or make a branch. The cables and the splices may be located above ground, underground, in conduits or in other environments either inside or outside buildings, but wherever they are located there is always the risk of ingress of environmental agents such as moisture or dust. In addition, underground installations are also subject to pressure, particularly hydrostatic pressure, whilst above ground installations suffer from diurnal thermal variations and other effects such as vibration, the risk of impacts or other disturbing forces.
In order to provide environmental protection for splices in cables or other elongate articles various protective measures are known. Systems utilising an enclosing casing have been found to be particularly valuable, such casings being enclosed containers having a housing for enclosing the cable connections or splices and at least one aperture in the housing wall through which the cable or cables can extend. Naturally, in order to prevent contamination by external agents, it is necessary to form a secure seal between the casing and any cable passing through it.
In some cases the opening has to be large enough to accommodate several cables although often a smaller number, less than the full complement, is used in practice. Such situations provide particular difficulties in forming a good seal because not only the size but also the cross sectional shape of a bundle of cables will vary in dependence on the actual number of cables used.
The Applicant""s international patent application WO97/45904 describes such a seal and a casing forming a cable closure in which the space between a cable passing through an opening and the opening itself is occupied with a gel held under pressure by a spring or other resilient means. This device, however, was particularly adapted to be used in circumstances where a single cable passes through each individual opening in the casing, so that the body of gel provided for engagement with the cable surface can be preliminarily shaped approximately to match the surface of the cable. This system works well and effectively, but cannot be immediately applied to casings in which the number of individual cables which may pass out through an opening cannot be determined in advance and for which, for reasons of production economy, it is appropriate to produce a modular casing capable of accommodating a range of cable configurations.
The Applicant""s international patent application PCT/GB99/01898 discusses one attempt to accommodate a situation where a plurality of cables pass out through an opening. This is achieved by providing a core or plug body having a plurality of channels and an associated sealant element the shape of which substantially matches that of the opening into which the sealant element is to be fitted such that, when a cable is fitted into one of the channels of the sealant element, the sealant is deformed and can be compressed in such a way as to form a seal between the cable and the opening.
The present invention is directed at substantially the same problem but provides an alternative solution in which, nevertheless, a good seal between an opening and an unspecified number of elongate elements such as cables may be achieved quickly and economically.
The Applicant""s U.S. Pat. No. 5,776,277 discloses a sealing device comprising flexible ribs which in use extend at least part around the periphery of each substrate so as to provide a sealing block between the elongate substrates and the housing. Foam blocks minimise any movement of the ribs along the body of the device but have no sealing function. Although this known device functions satisfactorily, it was found that its sealing capabilities could still be improved on.
According to one aspect of the present invention, therefore, a seal element for a closure having an opening through which more than one elongate article may project comprises a body having a plurality of axially extending radially projecting ribs defining, between circumferentially adjacent pairs thereof, locations for receiving one or more said elongate members, and is according to the present invention characterised in that the body comprises longitudinally adjacent parts of resilient material and sealant material.
In use of the seal element of the present invention elongate elements such as cables can be laid into the locations between circumferentially adjacent pairs of ribs in contact with the sealant material. As will be described in more detail below, a further sealant element may then be wrapped around the sealant part of the seal element and the whole assembly fitted into an opening in a casing. This offers a convenient way in which the elongate elements or cables can be held separate from one another which is advantageous in allowing the sealing pressure of the sealant material to be well transferred between them. A single shape and size of seal element can be made for use with a range of sizes of opening, and is capable of accommodating a range of sizes of cable as well as an unspecified number of cables.
In a preferred embodiment of the invention the said ribs have opposite faces which are substantially parallel, the resilient and sealant parts thereof being substantially flush with one another. It would, of course, be possible for the sealant part of the element to have a different shape from that of the resilient part, and in particular to project radially such as to require deformation as an elongate element is positioned into one of the locations between adjacent ribs.
Preferably the ribs are substantially flat although convex or concavely curved ribs may be utilised in certain circumstances.
Likewise, it is convenient if the opposite faces of the ribs converge radially outwardly. Such convergence is preferably at an extremely acute angle of only a few degrees.
The sealant part of the body is preferably a gel and suitable gel materials are known, for example, from our earlier international patent application WO97/45904.
The resilient part of the seal body may be a natural or synthetic elastomer. A preferred embodiment is formed with five said radially projecting ribs and the material of both the resilient part or parts and the sealant parts or parts is such that it can be severed with a cutting instrument.
The present invention also comprehends an assembly for making a seal between an opening through which one or more elongate articles may project, and the articles themselves, comprising a seal element in the form of a body having a plurality of axially extending radially projecting ribs defining between circumferentially adjacent pairs thereof, locations for receiving one or more said elongate members, the body comprising longitudinally adjacent parts of resilient material and sealant material, at least one retainer or tie strap for retaining the elongate articles in position between respective pairs of ribs, and an elongate strip of sealant material to be wrapped around the elongate articles at an axial location corresponding to that of the part of the body composed of sealant material.
The assembly may further comprise an elongate, substantially rigid reinforcing member positionable alongside an elongate element or in a vacant location between two adjacent ribs in a completed seal. Such a reinforcing member is of particular value in circumstances where there may be fewer cables than the minimum number of locations between ribs which it is convenient to provide. This reinforcing member can then be laid in the vacant location and acts as a reaction member against which the retaining member can act in holding together the elongate elements to retain them in the locations between the ribs.
Preferably an assembly for forming a seal also comprises retainers or tie straps for encircling the elongate elements (and, if provided, the rigid reinforcing member or members) at a position axially spaced from the seal body at each end thereof.
The assembly may, likewise, further include an adhesive strip for encircling the sealant strip and retaining it in position around the said elongate elements and the body of the seal element.
In a practical embodiment there is further provided at least one tension resistant retainer which can be fitted so as to extend circumferentially around the elongate elements and the resilient part of the seal element, acting to hold them together whereby to transfer axial loads from one to the other. Such tension resistant retainers are sometimes known as axial pull tapes and suitable examples will be described hereinafter in more detail. One such suitable tension resistant retainer comprises a strip of malleable material having surface formations such as to grip the said resilient part of the seal element when located circumjacently thereabout.
The present invention also comprehends a method of forming a seal for sealing between an opening and a plurality of elongate elements passing through the opening, comprising the steps of assembling the elongate elements with a seal element comprising a body having a plurality of axially extending radially projecting ribs defining between circumferentially adjacent pairs thereof locations for receiving one or more said elongate members, the body comprising longitudinally adjacent parts of resilient material and sealant material, with each elongate element received in a respective location between two adjacent elongate ribs of the seal element and extending there along, encircling the elongate elements with a retainer to secure them in position in the said locations, severing that part of each rib projecting radially beyond the elongate elements and applying an elongate strip of sealant circumferentially around the assembly in axial juxtaposition with the sealant part of the body to form a surrounding band of sealant the dimensions of which are not less than those of the opening to be sealed.
It is of value to be able to provide a universal seal element having a given number of ribs which may be greater than is always required. The method of the present invention thus includes the step of preparing the seal element by removing one or more ribs to provide a number of locations appropriate for the number of elongate elements to be received in the said locations thereof.
Thus, for example, if the seal element has five ribs, therefore defining five locations between circumferentially adjacent pairs of ribs, and it is only required to locate three cables, two of the ribs may be removed at or adjacent their roots to provide three locations for cables.
In some circumstances it may not be appropriate to position a cable in every location, for example if only two cables are to be utilised, because it is impracticable to cut down a seal element to fewer than three ribs. In such circumstances there may be provided a supplementary element to be received in a location not required for an elongate member around which the retainer member passes to retain the elongate elements in position in the locations.
Alternatively, one of the ribs of at least one part is at both ends provided with axially extending retaining bodies for retaining the elongate articles in their respective locations. This allows a better defined position of the seal element relative to the elongate articles, even when only one rib is used and the other ribs have been cut away.